CEI CEI Motor & Motor Control Inspection 2 — Questions and Answers
Question 1: NEC Article 440 applies specifically to which type of equipment?
- General-purpose motors over 5 hp
- Air-conditioning and refrigeration equipment (Correct answer)
- Industrial motor control centers
- Crane and hoist motors
Correct answer: Air-conditioning and refrigeration equipment
NEC Article 440 covers air-conditioning and refrigerating equipment, including hermetic refrigerant motor-compressors.
Question 2: When inspecting a motor control center (MCC), which grounding method is required for the MCC enclosure?
- A separate equipment grounding conductor to each unit
- A common ground bus bonded to the enclosure (Correct answer)
- Individual ground rods at the base of the MCC
- No grounding is required for MCC enclosures
Correct answer: A common ground bus bonded to the enclosure
NEC 408.40 requires motor control centers to have a main bonding jumper or equipment grounding conductor connecting the grounding bus to the enclosure.
Question 3: What is the purpose of a motor controller as defined in the NEC?
- To protect the motor from overloads only
- To start and stop the motor and protect it from overloads
- To disconnect the motor from the power source only
- To govern the starting, stopping, and speed of a motor (Correct answer)
Correct answer: To govern the starting, stopping, and speed of a motor
Per NEC Article 100, a controller is a device that governs, in a predetermined manner, the electric power delivered to the apparatus it controls.
Question 4: Which NEC section requires a readily accessible means to disconnect a motor from all ungrounded supply conductors?
- NEC 430.74
- NEC 430.102 (Correct answer)
- NEC 430.109
- NEC 430.110
Correct answer: NEC 430.102
NEC 430.102 requires a disconnecting means to be located in sight from the motor and driven machinery and to be readily accessible.
Question 5: An inspector finds a 10 hp, 480V, 3-phase motor with no overload protection installed. Under NEC 430.32, the MAXIMUM allowable overload device setting for this motor (FLA = 14A) is:
- 14.0 A
- 17.5 A (Correct answer)
- 21.0 A
- 25.0 A
Correct answer: 17.5 A
NEC 430.32(A)(1) allows overload protection at not more than 125% of the motor's full-load current for motors with a service factor of less than 1.15, so 14A × 1.25 = 17.5A.
Question 6: When inspecting a reduced-voltage motor starter, what is the primary reason for using this type of starter?
- To reduce the motor's operating temperature
- To limit inrush current during motor starting (Correct answer)
- To increase motor efficiency at full load
- To provide overload protection
Correct answer: To limit inrush current during motor starting
Reduced-voltage starters are used to limit inrush (locked-rotor) current during motor starting, reducing demand on the electrical system.
CEI CEI Motor & Motor Control Inspection 2
NEC Article 440 applies specifically to which type of equipment?